The present invention generally relates to a transmission apparatus and a transmission system used in a television conference and the like, for synthesizing image signals derived from a plurality of TV cameras positioned at a large number of places, and for outputting the synthesizing image signals. More specifically, the present invention is directed to a multiplexing transmission apparatus and system for an image signal, in which small images (will be referred to "small frames" hereinafter) which have been sent out from a plurality of TV cameras via encoding apparatuses at independent time intervals in the asynchronous mode, are synthesized into a single image (will be referred to a "large frame" hereinafter) in accordance with a predetermined rule, and also such a control operation is carried out that a synchronized image can be reproduced, as viewed from a reproducing side.
A conventional multiplexing apparatus has such an arrangement as shown in FIG. 1, which is employed in a TV conference system for synthesizing image signals derived from a plurality of TV cameras to be outputted.
(1) At a transmission side, each of image signals picked-up by a plurality of television cameras (will be also referred to "transmission terminals" hereinafter) 1-1, 1-2, . . . , 1-n, is encoded by encoding circuits 2-1, 2-2, . . . , 2-n. The encoded image signals are temporarily stored into smoothing memories so-called as a "FIFO" (simply, referred to a "FIFO") 3-1, 3-2, . . . , 3-n, and are read out therefrom at a constant speed. Then, the read image signals are transmitted to transmission paths 4-1, 4-2, . . . , 4-n.
(2) In the multiplexing apparatus 5, the code words transmitted from the transmission paths 4-1, 4-2, . . . , 4-n are temporarily stored in delay compensating circuits 6-1, 6- 2, . . . , 6-n. Subsequently, the code words are read out from the respective delay compensating circuits 6-1, 6-2, . . . , 6- n, and the read code words are sent out to the transmission path 11 at a constant speed and then transmitted to the reception terminal 14.
(3) At the reception side, after the speed control has been performed by the FIFO 12, the code words are read out, and then the original large frame is reproduced by the decoding circuit 13 to be displayed on the display apparatus 14.
The above-described conventional multiplexing apparatus is opened in, for instance, JP-A-3-6190.